1. Field of the Invention
This invention relates to alignment of optical devices. More particularly, this invention relates to a method, and the apparatus used therefor, for the axial alignment of the end face of an optical fiber or an array of optical fibers with a cylindrical lens and for evaluating the quality of the light that is emitted by the fiber or the array.
2. Description of the Related Art
In the past, the assembly and manufacture of optical assemblies having a linear array of optical elements has been time consuming and prone to quality control problems. The latest developments in optical cross-connect assemblies have only magnified these problems. Precisely engineered optical receiver arrays are required in these assemblies. A general demand for more precisely constructed assemblies having greater reliability has translated into a demand for better manufacturing apparatus and processes
Optical devices of the type addressed by the present invention currently in use involve an array of optical fibers having light transmitted therethrough. In typical devices the light exiting the end faces of the fibers is scattered, and it is necessary to collect it using collimation lenses or focusing optics. The focusing optics may include a precisely aligned cylindrical lens.
In current devices, it is required to precisely position a light source, which can be an optical fiber, or an array of optical fibers with respect to a horizontally oriented cylindrical lens within tolerances of a few microns in the vertical axis. It would be desirable to evaluate the quality of light that is emitted by the source at the time the alignment is performed, since setup costs have already been incurred. This would avoid the cost of performing a separate quality control procedure.
It is therefore a primary object of some aspects of the present invention to provide an improved method for precisely aligning a cylindrical lens with a fiberoptic array.
It is another object of some aspects of the present invention to provide an improved method for the evaluation of a beam emitted by a light source in an optical assembly
These and other objects of the present invention are attained by an optical arrangement in which the vertical alignment of an optical assembly is evaluated and adjusted. The assembly includes an array of emitters, such as an array of optical fibers, and a cylindrical lens. An optical stage or a vacuum chuck is used to adjust the vertical position of either the emitter or the cylindrical lens. Evaluation of alignment and beam quality is achieved using a defocused diffraction pattern produced by the cylindrical lens that is imaged onto the detector plane of a camera, and is captured by the camera. The output of the camera is linked to a display monitor, enabling qualitative evaluation of the image. A computer having a display monitor is also linked to the camera, using a frame grabber, and produces a plot of a vertical profile of the camera image The relative vertical position of the emitter and the cylindrical lens is then adjusted until the diffraction peaks seen on the computer monitor are symmetric and have the same amplitude. Using qualitative evaluation the source of defects can be differentiated by translating the cylindrical lens along its longitudinal axis.
The invention provides a method for aligning an optical assembly, including the steps of emitting a beam from an emitter, and disposing a cylindrical lens in the beam to form a diffraction pattern which is imaged onto the detector plane of a camera, wherein the longitudinal axis of the cylindrical lens is horizontally oriented. The method includes displaying a vertical profile of the line image, defocusing the line image until a first peak and a second peak of the profile are displayed, and adjusting the vertical position of the cylindrical lens relative to the emitter until the first peak and the second peak are symmetric.
In an aspect of the method, adjusting the vertical position is performed until the amplitude of the first peak is identical to the amplitude of the second peak.
According to a further aspect of the method, the line image is captured on a camera, which may be an infra-red camera.
In yet another aspect of the method, the profile is displayed by connecting a computer to the camera.
According to still another aspect of the method, the emitter includes a fiberoptic array.
One aspect of the method includes detecting an irregularity in the line image, horizontally displacing the cylindrical lens in a direction of its longitudinal axis, and determining a positional change of the irregularity.
According to an additional aspect of the method, the irregularity is detected by visual inspection.
According to one aspect of the method, the irregularity is detected by automatic computer implemented pattern recognition.
According to another aspect of the method, the beam includes a first beam that is emitted from a first element of the emitter, and a second beam that is emitted from a second element of the emitter. The line image includes a first line image that is projected by the first beam, and a second line image that is projected by the second beam The profile includes a first profile of the first line image and a second profile of the second line image. The method includes performing a xcex8Z movement of the emitter relative to the cylindrical lens until the first peak and the second peak of the first profile, and the first peak and the second peak of the second profile are simultaneously symmetric.
According to an additional aspect of the method, the beam includes a first beam that is emitted from a first element of the emitter and a second beam that is emitted from a second element of the emitter. The line image includes a first line image that is projected by the first beam, and a second line image that is projected by the second beam. The profile includes a first profile of the first line image and a second profile of the second line image. The method includes adjusting the first line image to produce a predetermined pattern, performing a xcex8Y movement of the emitter relative to the cylindrical lens until the first line image and the second line image simultaneously have the predetermined pattern.
According to another aspect of the method, the predetermined pattern is a unimodal peak on the first profile and the second profile.
According to a further aspect of the method, the predetermined pattern is a multimodal peak on the first profile and the second profile.
The invention provides a method for aligning an array of optical fibers with a lens, including the steps of horizontally orienting a longitudinal axis of a cylindrical lens emitting a first beam from a first optical fiber of an optical fiber array, disposing the cylindrical lens in the first beam to form a first line image, displaying a first vertical profile of the first line image, defocusing the first line image until a first peak and a second peak of the first vertical profile are displayed, and adjusting a vertical position of the cylindrical lens relative to the optical fiber array until the first peak and the second peak are symmetric.
According to an aspect of the method, adjusting the vertical position is performed until the amplitude of the first peak is identical to the amplitude of the second peak.
According to one aspect of the method, the first line image is captured on a camera, which may be an infra-red camera
According to a further aspect of the method, the first vertical profile is displayed by connecting a computer to the camera.
Yet another aspect of the method includes detecting an irregularity in the first line image, horizontally displacing the cylindrical lens in a direction of the longitudinal axis, and determining a positional change of the irregularity.
According to yet another aspect of the method, the irregularity is detected by visual inspection.
According to still another aspect of the method, the irregularity is detected by automatic computer implemented pattern recognition.
An additional aspect of the method includes emitting a second beam from a second optical fiber of the optical fiber array toward the cylindrical lens to form a second line image, and displaying a second vertical profile of the second line image. The method includes performing a xcex8Z movement of the optical fiber array relative to the cylindrical lens until the cylindrical lens and the optical fiber array are rotationally aligned, such that the first peak and the second peak of the first vertical profile are symmetric, and the first peak and the second peak of the second vertical profile are symmetric.
According to another aspect of the method, the first optical fiber and the second optical fiber are alternately illuminated by a light source.
One aspect of the method includes adjusting the first line image to produce a predetermined pattern, emitting a second beam from a second optical fiber of the optical fiber array toward the cylindrical lens to form a second line image, displaying a second vertical profile of the second line image The method includes performing a xcex8Y movement of the optical fiber array relative to the cylindrical lens until the cylindrical lens and the optical fiber array are rotationally aligned, such that the first line image and the second line image have the predetermined pattern.
According to a further aspect of the method, the first optical fiber and the second optical fiber are alternately illuminated by a light source.
According to another aspect of the method, the predetermined pattern is a unimodal peak.
According to a further aspect of the method, the predetermined pattern is a multimodal peak.